1. Field of the Invention
The present invention relates to polynucleotides corresponding to the nadA gene and which encode the quinolinate synthetase A protein, methods of producing nicotinic acid or nicotinic acid derivatives, and methods of screening for polynucleotides which encode proteins having quinolinate synthetase A activity.
2. Discussion of the Background
Nicotinic acid and nicotinic acid derivatives are used in human medicine, in the pharmaceuticals industry, in the foodstuffs industry and in animal nutrition. It is known that L-amino acids are prepared by fermentation from strains of coryneform bacteria, in particular Corynebacterium glutamicum. Prior to the present invention there were no processes for the preparation of nicotinic acid or nicotinic acid derivatives using coryneform bacteria.
The inventors had the object of providing processes for the fermentative preparation of nicotinic acid and nicotinic acid derivatives.
Accordingly, one object of the present invention is an isolated polynucleotide which encodes a protein comprising the amino acid sequence of SEQ ID NO:2.
Another object of the present invention is the nucleotide sequence of SEQ ID NO:1.
Another object of the present invention are isolated polynucleotides which are complimentary to SEQ ID NO:1 or a 70%, 80% or 90% identical to SEQ ID NO:1.
Another object of the present invention are isolated polynucleotides which hybridizes under stringent conditions to SEQ ID NO:1.
Another object of the present invention are polynucleotides which comprises at least 15 consecutive nucleotides of SEQ ID NO:1.
Another object of the present invention are vectors and host cells containing the polynucleotides. In a preferred embodiment the host cells are Corynebacterium and are preferably Corynebacterium glutamicum. 
Another object of the present invention is a Coryneform bacterium which has an enhanced nadA gene.
Another object of the present invention is to a process for producing nicotinic acid or a nicotinic acid derivative culturing a host cell in accordance with the invention in a medium suitable for the expression of the polynucleotide; and collecting the nicotinic acid or nicotinic acid derivative. In a preferred embodiment, the nicotinic acid or nicotinic acid derivative is concentrated after it is collected. In another embodiment, the host cell can also contain an pyc, zwa1 and/or prs whose expression is enhanced; and/or an pck, poxB and zwa2 whose expression is attenuated.
Another object of the present invention is a process for screening for polynucleotides which encode a protein having quinolinate synthetase A activity by hybridizing one or more of the polynucleotides embodied in this application to the polynucleotide to be screened; expressing the polynucleotide to produce a protein; and detecting the presence or absence of quinolinate synthetase A activity in said protein.